Polyvinyl chloride resins (hereinafter referred to as "PVC resins") are excellent in terms of strength, processability, and living body safety and are economical advantageous. Thus, PVC resins have generally been used in the medical field such as for infusion bags, artificial dialysis circuits, catheters, etc.
It is sometime necessary, depending on the use, to combine PVC resin with other chemicals so as to provide the PVC resins with pharmaceutical effects which are not inherent to the PVC resins. Various methods have been employed therefor.
For example, Japanese Patent Application (OPI) No. 65009/84 and U.S. Pat. No. 4,555,398 disclose a method of adding and kneading a vasodiolator to a PVC resin or similar resin thereby obtaining a slow releasing effect for the vasodiolator. Although the method is simple and excellent from an economical point of view, it is difficult to control the slow releasing rate of the pharmaceutical substance since the vasodiolator itself is merely added and dispersed In this case, the pharmaceutical substance is disadvantageously released in a relatively short period of time.
Japanese Patent Application (OPI) No. 14358/82 discloses a method of coating a resin comprising a hydrophobic polymer graft-complymerizing thereon a hydrophilic monomer to the surface of PVC resins and ionically bonding the coating polymer with heparin as an anticoagulant. Although the slow releasing property of heparin from the composition obtained by this method is satisfactory, the steps of grafting and ionically bonding are complicated and thus is economically disadvantageous.
Japanese Patent Application (OPI) No. 45537/87 discloses a method of adding and dispersing porous power, which is previously impregnated with a phaumaceutical solution into fine pores thereof, to a matrix resin thereby providing the slow releasing property of the pharmaceutical substances. Although this method is simple in production step and excellent in slow releasability of the pharmaceutical substance, if a PVC resin is used as the matrix resin, there is a problem in that this method can not be applied to thermally instable substances, for example, heparin or urokinase since the processing temperature for the PVC resin is as high as from 150 to 190.degree. C. in the usual melt kneading or paste processing step.
Although a solution method of dissolving PVC resins in an organic solvent may be used as a PVC resin processing method which needs no heating, the polymerization degree of the PVC resin used is limited in view of its solubility. This results in problems, i.e., the strength and the impurity leaching property as a medical material are insufficient. In addition, it cannot be used in extrusion molding since the material drips from a nozzle because of the low viscosity of the solution containing the organic solvent